Dependence of the optical properties of Fe<Subscript>78</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy on its structural state

The optical properties of Fe₇₈Si₁₀B₁₂ ferromagnetic alloy in amorphous, crystalline, and intermediate structural states have been investigated by ellipsometry in the spectral range of 0.22–18 μm. It is established that alloy crystallization leads to a significant change in the optical constants and the frequency dependences of the dielectric functions calculated based on these optical constants. The structural reconstruction under heat treatment leads to an increase in the intensity and shift of interband absorption bands. The plasma and relaxation frequencies of conduction electrons are determined; their numerical values also depend on the degree of atomic ordering.     

Chemical Structure of Fe<Subscript>78</Subscript>B<Subscript>13</Subscript>Si<Subscript>9</Subscript> Alloy Surface Layers in the Solid and Liquid States

The chemical structure of Fe₇₈B₁₃Si₉ alloy in the solid and liquid states and local atomic environment are studied in situ by X-ray photoelectron spectroscopy (XPS). The chemical bonds between elements in the melt are analyzed during a temperature increase. Two temperature regions are identified. The liquid surface in the first temperature region is shown to contain clusters of Fe-Si and (Fe-O _x )-Si types. In the second one, clusters of Fe-B and (Fe-O _x )-B types dominate. It is impossible to determine the composition of the clusters definitively using XPS data only. A jump-like change in the composition of the surface layers of the melt is detected, which is interpreted as structural transformations within the liquid state.     

Effect of uniaxial tension and hydrostatic compression on the geometry and morphology of amorphous Fe<Subscript>77</Subscript>Ni<Subscript>1</Subscript>Si<Subscript>9</Subscript>B<Subscript>13</Subscript> alloy ribbon surface

The effect of hydrostatic pressure and uniaxial compression on the relief of an amorphous Fe₇₇Ni₁Si₉B₁₃ alloy ribbon surface was studied using scanning tunneling and atomic-force microscopy. The fracture surfaces of samples were also studied. It is found that both the initial surfaces and the surfaces of samples subjected to hydrostatic compression or tension, as well as fracture surfaces, are fractal or multifractal, but their fractality parameters are different. Hydrostatic pressure decreases the surface roughness and the average fractal dimension of the surface on both sides of the ribbons. The dependence of the surface fractal characteristics on tension is more complex. Prior to the occurrence of a “critical event” on the surface (formation of a deformation band or a through crack), the Hölder index and the half-width of the singularity spectrum decrease. The correlation is discussed between the fractal characteristics of the ribbon surface and those of a fracture surface, and the role of an excess free volume in the initiation of fracture of amorphous alloys is analyzed.     

Effect of nanocrystallization on the mechanical and magnetic properties of finemet-type alloy (Fe<Subscript>78.5</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript>)

The kinetics of primary crystallization and the effect of structural parameters of the precipitating nanocrystalline α-phase Fe-Si on changes in microhardness, coercive force, and saturation magnetization in an amorphous Finemet-type 5BDSR alloy (Fe_78.5Si_13.5B₉Nb₃Cu₁) obtained by melt quenching are studied. It is found that both an increase in bulk density and an increase in the average nanoparticle size contribute to the hardening of the amorphous/nanocrystalline alloy.     

Effect of external actions on the magnetic properties and corrosion resistance of Co<Subscript>70.5</Subscript>Fe<Subscript>0.5</Subscript>Cr<Subscript>4</Subscript>Si<Subscript>7</Subscript>B<Subscript>18</Subscript> amorphous alloy

Variations in the magnetic characteristics (specific saturation magnetization and coercive force) of Co–Fe–Cr–Si–B amorphous alloy (AA) are studied after high-pressure torsion (HPT) and heat treatment. The behavior of AA magnetic properties is analyzed with respect to structural transformations caused by external actions. The corrosion resistance of AA upon transitioning from an amorphous to a crystalline state is investigated. The established optimum annealing and HPT conditions yield a satisfactory combination of the magnetic properties and corrosion resistance of the investigated alloy.     

The temperature dependence of the magnetoelastic characteristics of cores for force sensors utilizing Fe<Subscript>70</Subscript>Ni<Subscript>8</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy

This paper presents the results of investigation on the influence of temperature on magnetoelastic characteristics of the two ring-shaped cores, made of Fe₇₀Ni₈Si₁₀B₁₂ amorphous alloy. The cores were annealed for 1 h at 350 and 400°C, respectively. The compressive force F was applied perpendicular to the direction of the magnetizing field H in the sample. Special cylindrical backing enables application of the uniform compressive stress σ to the wound ring sample. A resistive furnace heated the experimental set-up. Results presented in the paper indicate a significant influence of the temperature on the magnetoelastic characteristics of Fe₇₀Ni₈Si₁₀B₁₂ amorphous alloy. Information about the magnetoelastic characteristics of this material may be useful in the magnetoelastic sensor development. Also this will create new possibilities in the development of physical model of magnetoelastic effect.      

One-dimensional AGMI sensor with Co<Subscript>66</Subscript>Fe<Subscript>4</Subscript>Si<Subscript>15</Subscript>B<Subscript>15</Subscript> ribbon as sensing element

A novel asymmetric giant magneto impedance (AGMI) sensor was developed and the performance of the sensor was carefully studied. This one dimensional sensor can be further developed as a two-dimensional compass that can be used for navigational purposes. We used commercial Metglas 2714A ribbon. The sensor uses Co₆₆Fe₄Si₁₅B₁₅ ribbon as a sensing element. The results showed for high sensitivity and resolution. The GMI sensor consists of a crystal oscillator voltage to current converter for providing the current to the sample, a differential amplifier, successive amplifier stages, multiplier, and cascaded low-pass filters. The observed sensitivity was 25 V/Oe. Angle sensitivity was found to be 2 mV/degree. Our sensor showed excellent linearity when compared with previous sensors [13, 14]. These sensors require dc bias coils and two sensor elements to attain good linearity. PACS 85.75.Ss; 85.70.Ay; 85.70.-w; 85.75.-d; 75.30.Gw; 75.50.Kj; 75.90.+w     

Properties of ferromagnetic resonance in Fe<Subscript>73.5</Subscript>CuNb<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> nanocrystalline alloys

The structural properties and parameters of ferromagnetic resonance have been studied for Fe_73.5CuNb₃Si_13.5B₉ nanocrystalline alloys produced from the initial amorphous state via annealing under different conditions. The dependence of the linewidth of the ferromagnetic resonance on the grain size ΔH ∼ D ⁶ has been found. The result is discussed within the framework of the random magnetic anisotropy model.     

Long-wavelength magnetic excitations in the Fe<Subscript>65</Subscript>Ni<Subscript>35</Subscript> alloy

A theoretical analysis of small-angle neutron scattering is performed for the Fe₆₅Ni₃₅ alloy at a temperature T=0.9T _C =450 K. The results obtained indicate the existence of long-wavelength magnetic excitations that do not correspond to spin waves of the Holstein-Primakoff type. The possible nature of these excitations is discussed.     

Magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> surface

The magnetic properties of the magnetite Fe₃O₄(110) surface have been studied by spin resolved Auger electron spectroscopy (SRAES). Experimental spin resolved Auger spectra are presented. The results of calculation of Auger lines polarization carried out on the basis of electronic state density are presented. Problems related to magnetic moments of bivalent (Fe²⁺) and trivalent (Fe³⁺) ions on the Fe₃O₄(110) surface are discussed. It is established that the deposition of a thin bismuth film on the surface results in significant growth of polarization of iron Auger peaks, which is due to additional spin-orbit scattering of electrons by bismuth atoms.     

High-temperature heat capacity of the Al<Subscript>63</Subscript>Cu<Subscript>25</Subscript>Fe<Subscript>12</Subscript> quasicrystal

The mechanisms of energy absorption by metallic alloys with long-range aperiodic lattice order and electronic properties of marginal metals are studied. The heat capacity and linear expansion coefficient of the Al₆₃Cu₂₅Fe₁₂ icosahedral phase in the temperature range 300–1000 K are measured for the first time. Disagreement between the measured heat capacity and predictions made from the Debye model is found and analyzed. It is shown that the excess heat capacity observed at the temperatures of the experiment is fitted by Einstein’s function in the approximation T

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Magnetic properties and the magnetoimpedance effect of nanostructured Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons with induced magnetic anisotropy

The structure and magnetic properties and the magnetoimpedance effect of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy ribbons, obtained from the amorphous state by annealing under different conditions, were comparatively analyzed. Despite the similarity of the samples’ structural states and the processes of their quasi-static magnetization reversal, the features of the magnetoimpedance effect are indicative of significant differences in the processes of their dynamic magnetization.     

Magnetic domain and local atomic structures of the Fe<Subscript>0.94</Subscript>Si<Subscript>0.06</Subscript> alloy before and after thermomagnetic treatment in an alternating-current magnetic field

The changes observed in the local atomic structure of an iron alloy with 6 at % Si as a result of thermomagnetic treatment in an alternating-current magnetic field and their correlation with magnetic characteristics, such as the domain structure and magnetic properties, have been investigated using Mössbauer spectroscopy. It has been shown that the destabilization of the domain structure is caused by the destruction of uniaxial magnetic anisotropy in domains due to a disordered distribution of pairs of silicon atoms along the 〈100〉 easy magnetization axes. Annealing and cooling without an external magnetic field and in an alternating-current magnetic field lead to a change in the magnetic texture of single-crystal samples of the siliconiron alloy. When the samples are annealed in an alternating-current magnetic field, the magnitude of this effect depends on the orientation of the magnetic field with respect to the crystallographic axes of the sample.     

The evolution of electronic configuration and magnetic characterization of Fe<Subscript>9</Subscript>Ni<Subscript>1</Subscript>, Fe<Subscript>8</Subscript>Ni<Subscript>2</Subscript> alloy in theoretical calculation

To analyze the origin of the magnetic enhancement of Fe-Ni alloy, the electronicconfigurations and magnetic properties were investigated using density functional theorybased on the first-principle. The supercell (5 × 1 × 1) of Fe,Fe₉Ni₁ and Fe₈Ni₂ were constructed. Thedefect formation energy, band structure, density of states and electron density differencewere calculated. The results showed that Ni doping changed the electronic configuration ofFe atoms, resulting in the enhancement of spin polarization of Fe and the larger Bohrmagnetic moment in Fe-Ni alloys (Fe₉Ni₁). The results showed thatthe charge transfer and the atomic spacing between Fe atoms and the dopant Ni atoms playedan important role in determination of magnetic moment. The value of Fe supercell(5 × 1 × 1), Fe₉Ni₁ and Fe₈Ni₂ were 23.14,23.34 and 22.61μ _B, respectively.     

Effect of temperature on the magnetoimpedance of an elastically deformed Fe<Subscript>4</Subscript>CO<Subscript>67</Subscript>Mo<Subscript>1.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>11</Subscript> foil

The effect of temperature and elastic tensile stresses on the magnetoimpedance of an amorphous Vitrovac 6025Z (Fe₄CO₆₇Mo_1.5Si_16.5B₁₁) foil is studied. Two temperature ranges (20–70 and 70–220°C) in which the effect of elastic tensile stresses on the magnetoimpedance has different characters are detected. The existence of these two temperature ranges is shown to be caused by a change in the sign of a magnetostriction constant at 70°C.     

Atomic and magnetic structures of Fe<Subscript>70</Subscript>Al<Subscript>5</Subscript>B<Subscript>25</Subscript> amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe₇₅B₂₅ and Fe₇₀Al₅B₂₅ amorphous alloys has been studied by ¹¹B and ²⁷Al nuclear magnetic resonance at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe₇₀Al₅B₂₅ alloy, gives rise to an additional contribution to the ¹¹B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the ⁵⁷Fe nuclei. In the Fe₇₀Al₅B₂₅ amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe₃B phase type.     

Temperature dependence of the magnetic properties and magnetoimpedance of nanocrystalline Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons

The temperature dependences of the magnetic properties and the magnetoimpedance effect of soft magnetic nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy ribbons are studied in the temperature range 24–160°C. A high temperature sensitivity of the impedance and the magnetoimpedance effect of the ribbons are detected in the ac frequency range 0.1–50 MHz. At an ac frequency of 50 MHz, the change in the impedance reaches 0.2 Ω/°C (0.5%/°C) in the temperature range 85–160°C. When the temperature increases, a monotonically decreasing character of the dependence of the magnetoimpedance effect on the applied magnetic field changes into a dependence having an increasing initial segment. The effect of temperature on the magnetoimpedance properties of the soft magnetic nanocrystalline ribbons is shown to result from temperature-induced changes in their electrical conductivity, magnetization, and effective magnetic anisotropy.     

The Optical Gain of a Si-Based Lattice-Matched Si<Subscript>0.15</Subscript>Ge<Subscript>0.621</Subscript>Sn<Subscript>0.229</Subscript>/Si<Subscript>0.637</Subscript>Ge<Subscript>0.018</Subscript>Sn<Subscript>0.345</Subscript> MQW Laser

We study the optical-gain characteristics of a Si-based MQW laser, in which the active region has 20 Si_0.15Ge_0.621Sn_0.229 quantum wells separated by 20 Si_0.637Ge_0.018Sn_0.345 barriers. We reach a maximum optical gain of 2300 cm^?1 with an estimated carrier concentration of 5·10¹⁸ cm^?3, which is equivalent to the transparent current density equal to 0.5 kA/cm². Furthermore, we discuss the optical confinement factor and modal gain. The modal gain depends sensitively on the number of the quantum wells (QWs), and this fact restricts the optical confinement factor. The modal gain of the model we proposed can reach 1500 cm^?1 at the injection current density equal to 3 kA/cm². We hope that our results show the possibility to obtain a Si-based near-infrared laser.     

Nanocrystallization of an amorphous Fe<Subscript>80</Subscript>B<Subscript>20</Subscript> alloy during severe plastic deformation

The structural evolution of an amorphous Fe₈₀B₂₀ alloy subjected to severe plastic deformation at room temperature or at 200°C was studied. Deformation leads to the formation of α-Fe nanocrystals in an amorphous phase. After room-temperature deformation, nanocrystals are localized in shear bands. After deformation at 200°C, the nanocrystal distribution over the alloy is more uniform. Possible causes of the crystallization of the amorphous phase during severe plastic deformation are discussed.